Commit 1b8ab815 authored by Erez Zadok's avatar Erez Zadok Committed by Al Viro

VFS/fsstack: handle 32-bit smp + preempt + large files in fsstack_copy_inode_size

Copy the inode size and blocks from one inode to another correctly on 32-bit
systems with CONFIG_SMP, CONFIG_PREEMPT, or CONFIG_LBDAF.  Use proper inode
spinlocks only when i_size/i_blocks cannot fit in one 32-bit word.
Signed-off-by: default avatarHugh Dickins <>
Signed-off-by: default avatarErez Zadok <>
Signed-off-by: default avatarAl Viro <>
parent 9afa2fb6
......@@ -7,10 +7,58 @@
* This function cannot be inlined since i_size_{read,write} is rather
* heavy-weight on 32-bit systems
void fsstack_copy_inode_size(struct inode *dst, const struct inode *src)
void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
i_size_write(dst, i_size_read((struct inode *)src));
dst->i_blocks = src->i_blocks;
loff_t i_size;
blkcnt_t i_blocks;
* i_size_read() includes its own seqlocking and protection from
* preemption (see include/linux/fs.h): we need nothing extra for
* that here, and prefer to avoid nesting locks than attempt to keep
* i_size and i_blocks in sync together.
i_size = i_size_read(src);
* But if CONFIG_LBDAF (on 32-bit), we ought to make an effort to
* keep the two halves of i_blocks in sync despite SMP or PREEMPT -
* though stat's generic_fillattr() doesn't bother, and we won't be
* applying quotas (where i_blocks does become important) at the
* upper level.
* We don't actually know what locking is used at the lower level;
* but if it's a filesystem that supports quotas, it will be using
* i_lock as in inode_add_bytes(). tmpfs uses other locking, and
* its 32-bit is (just) able to exceed 2TB i_size with the aid of
* holes; but its i_blocks cannot carry into the upper long without
* almost 2TB swap - let's ignore that case.
if (sizeof(i_blocks) > sizeof(long))
i_blocks = src->i_blocks;
if (sizeof(i_blocks) > sizeof(long))
* If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for
* fsstack_copy_inode_size() to hold some lock around
* i_size_write(), otherwise i_size_read() may spin forever (see
* include/linux/fs.h). We don't necessarily hold i_mutex when this
* is called, so take i_lock for that case.
* And if CONFIG_LBADF (on 32-bit), continue our effort to keep the
* two halves of i_blocks in sync despite SMP or PREEMPT: use i_lock
* for that case too, and do both at once by combining the tests.
* There is none of this locking overhead in the 64-bit case.
if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
i_size_write(dst, i_size);
dst->i_blocks = i_blocks;
if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
......@@ -9,7 +9,7 @@
/* externs for fs/stack.c */
extern void fsstack_copy_attr_all(struct inode *dest, const struct inode *src);
extern void fsstack_copy_inode_size(struct inode *dst, const struct inode *src);
extern void fsstack_copy_inode_size(struct inode *dst, struct inode *src);
/* inlines */
static inline void fsstack_copy_attr_atime(struct inode *dest,
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